Shape memory polymers (SMPs) are uniquely suited to a number of applications due to their shape storage and recovery abilities and the wide range of available chemistries. However, many of the desired performance properties are tied to the polymer chemistry which can make optimization difficult. The use of foaming techniques is one way to tune mechanical response of an SMP without changing the polymer chemistry. In this work, a novel thiol-epoxy SMP was foamed using glass microspheres (40 and 50% by volume Q-Cel 6019), using expandable polymer microspheres (1% 930 DU 120), and by a chemical blowing agent (1% XOP-341). Each approach created SMP foam with a differing density and microstructure from the others. Thermal and thermomechanical analysis was performed to observe the behavioral difference between the foaming techniques and to confirm that the glass transition (T-g) was relatively unchanged near 50 degrees C while the glassy modulus varied from 19.1 to 345 MPa and the rubbery modulus varied from 0.04 to 2.2 MPa. The compressive behavior of the foams was characterized through static compression testing at different temperatures, and cyclic compression testing at T-g. Constrained shape recovery testing showed a range of peak recovery stress from 5 MPa for the syntactic Q-Cel foams to similar to 0.1 MPa for the chemically blown XOP-341 foam. These results showed that multiple foaming approaches can be used with a novel SMP to vary the mechanical response independent of T-g and polymer chemistry.

The proton-conductive doped ceramic materials, including SrCe0.95Tb0.05O3−δ (SCTb), SrCe0.8Zr0.1Y0.1O3−δ (SCZY), and SrZr0.95Y0.05O3−δ (SZY), are synthesized in the forms of nanoparticles and nanocrystalline thin films on sapphire wafers and long-period grating (LPG) fibers. The H2 chemisorption and electrical conductivity of the nanocrystalline SCTb, SCZY, and SZY materials are measured at high temperature with and without the presence of CO2 gas. The resonant wavelength shifts (\( \Updelta \lambda_{{{\text{R,H}}_{ 2} }} \)) of the SCTb, SCZY, and SZY thin-film coated LPGs in response to H2 concentration changes are studied in gas mixtures relevant to coal gasification syngas to evaluate their potential for high-temperature H2 detection. The results show that, at around 773.15 K (500 °C), SCTb has the highest H2 sensitivity but the most severe interferences from impurities such as CO2 and H2S; SZY has the best chemical resistance to impurities but the lowest H2 sensitivity; and SCZY exhibits high H2 sensitivity with reasonable chemical resistance.

This paper reports the fabrication and test of multilayer fiber optic sensors (FOSs) for hydrogen gas monitoring at high temperature. The FOS is a long-period fiber grating (LPFG) coated with a proton-conducting SrCe0.8Zr0.1Y0.1O2.95 (SCZY) nanocrystalline thin film and a chemically inert and thermally stable nanoporous silicalite protective layer. The multilayer sensors were tested for their responses to the variation of H2 partial pressure at 500°C. The sensor's H2-sensitivity increased with increasing the thickness of the SCZY sensing film and decreased with the thickness of the silicalite film. The silicalite overcoat had no appreciable influence on the sensor's response time because of the fast diffusion of the small H2 molecules in the zeolitic channels. Because of the uniform subnanometer sized pore opening, the silicalite layer is inaccessible to any fine particles or large contaminating molecules. The multilayer FOS is thus potentially useful for in situ H2 monitoring in the dusty syngas streams from coal or biomass gasification.

The overall goal of this project is to conduct fundamental studies on advanced ceramic materials and fiber optic devices for developing new types of high temperature (>500{degree}C) fiber optic chemical sensors (FOCS) for monitoring fossil (mainly coal) and biomass derived gases in power plants. The primary technical objective is to investigate and demonstrate the nanocrystalline doped-ceramic thin film enabled FOCS that possess desired stability, sensitivity and selectivity for in-situ, rapid gas detection in the syngas streams from gasification and combustion flue gases. This report summarizes research works of two integrated parts: (1) development of metal oxide solid thin films as sensing materials for detection and measurement of important gas components relevant to the coal- and biomass-derived syngas and combustion gas streams at high temperatures; and (2) development of fiber optic devices that are potentially useful for constructing FOCS in combination with the solid oxide thin films identified in this program.

Nanocrystalline copper-doped zirconia (CDZ; Cu:Zr=16:84) thin films have been synthesized on long-period fiber gratings (CDZ-LPFG) by a polymeric precursor method. The CDZ-LPFG device was demonstrated to have high sensitivity and good reversibility for low-concentration CO sensing at high temperatures. The CDZ-LPFG responds with red shifts of its resonant wavelength (λR) to CO-containing gases and the λR shift reverses when it is exposed to air. The optical response of the CDZ-LPFG to CO is due primarily to the CDZ refractive index variations resulted from the reversible redox reactions (i.e. Cu2+⇔Cu+) in reducing and oxidizing atmospheres. The magnitude of the λR shift exhibited a strong dependence on CO concentration in a range from 0 to 1000ppm that is potentially useful for quantitative measurement.

A ZSM-5 zeolite thin film with Si/Al ratio of about 23 has been grown on a long period fiber grating (LPFG) for optical gas sensing by monitoring its resonance wavelength (λR) shift caused by molecular sorption into the zeolite cavity. The sensing selectivity, sensitivity and speed of response of the zeolite-coated LPFG (Z-LPFG) are determined by the adsorption equilibria and transport properties of the analyte molecules in the zeolite pores. The ZSM-5 zeolite was modified through ammonium ion exchange and subsequent calcination to form acidic ZSM-5 (H-ZSM-5). The surface acidified Z-LPFG (HZ-LPFG) achieved dramatically improved sensitivity and selectivity for detecting ammonia gas. Also, increasing operation temperature improves sensing selectivity for the strongly adsorbing ammonia over weakly adsorbing gases and enhances response speed but compromises detection sensitivity due to reduced amount of adsorption for ammonia.

A fiber optical sensor has been developed by coating proton conducting perovskite oxide (Sr(Ce(0.8)Zr(0.1)) Y(0.1)O(2.95), SCZY) thin film on the long-period fiber grating (LPFG) for high temperature in situ measurement of bulk hydrogen in gas mixtures relevant to the fossil-and biomass-derived syngas. In this paper, we investigate in the H(2)-sensing mechanism of the SCZY-LPFG sensor. The high temperature H(2) adsorbance in the SCZY, the SCZY electric conductivity in H(2), and the resonant wavelength shift of the SCZY-LPFG (del lambda(R,H2)) have been experimentally studied to understand the effect of operation temperature on the sensor's sensitivity to H(2). Because of the activation process of the H(2) reaction with the perovskite oxide, increasing temperature benefits the H(2) uptake in the SCZY phase and the sensitivity of the SCZY-LPFG sensor. However, the thermal stability of the LPFG and the microstructure of the SCZY nanocrystalline film limit the application temperature of the fiber optic sensor.

MFE, a multivariate public key encryption scheme proposed by Wang et al in CT-RSA 2006, was conquered by second order linearization equation (SOLE) attack by Ding et al in PKC 2007. To resist this attack, many improved schemes were proposed. Wang et al in [WFW09 and Wang in [Wan07] both modified MFE and raised the public key from quadratic to quartic equations. We call the two quartic schemes Quartic-1 and Quartic-2 respectively for convenience. They are indeed immune to the SOLE attack. However, we find that there exist many quadratization equations (QEs), which are quadratic in plaintext variables and linear in ciphertext variables and can be derived from the public keys of Quartic-1 and Quartic-2. In this paper, we utilize QEs to recover the corresponding plaintext for a given ciphertext. For Quartic-1, we firstly find there are at least 2r SOLEs, which was regarded as impossible by the original authors, furthermore, we can find at least 35r QEs with a complexity $\mathcal {O}((90r^2(15r+1)+180r^2+15r(15r+1)/2+27r+1)^w)$ , where r is a small number denoting the degree of extension of finite fields and w ≈ 2.732. The computational complexity of deriving these equations is about 237. But to find the original plaintext, there still needs 240 times Gröbner basis computations, which needs practically 1.328 seconds each time. For Quartic-2, we make a theoretical analysis and find 18r QEs with a computational complexity $\mathcal {O}((15r+1)6r(12r+1)+180r^2+27r+1)^w$ . The complexity is 236 for the parameter proposed in [Wan07], and we can break the scheme practically in 3110.734 seconds. Finally, we show that another improved version of MFE in [WZY07] is insecure against the linearization equation attack although its authors claimed it is secure against high order linearization equation attack. Our attack on the two quartic schemes illustrates that non-linearization equations like quadratization equations which are not degree one in plaintext variables can also be used efficiently to analyze multivariate cryptosystems.

Dense nanocrystalline copper-doped zirconia (CDZ, Cu:Zr=16:84) thin film was coated on the surface of a 125 μm-diameter long-period fiber grating (LPFG) by a facile synthesis route involving polymeric precursor coating and subsequent thermal treatments. The CDZ film had a uniform thickness of ~100 nm and grain size of 20 to 35 nm after a brief annealing step at 700°C for 1 hour. This CDZ thin film coated LPFG (CDZ-LPFG) was evaluated at a high temperature of 550°C for its change of resonant wavelength (λR) in response to the variation of carbon monoxide (CO) concentration in nitrogen (N2). The λR was found to shift toward longer wavelength when increasing the CO concentration. The CDZ-LPFG sensor response was found to be reproducible and reversible at low level CO concentrations (<1,000 ppm) but became irreversible when the CO concentration was high (e.g. at 10,000 ppm). The high temperature stability of the CDZ material in CO-containing atmospheres was studied to understand the limit of CO measurement range.

There is a range of ways to couple light in a single mode fiber (SMF) from core mode to cladding modes, which can be applied in some fiber sensors. Recently, a very simple method using CO2 laser irradiation is put forward. By coupling core mode to cladding mode in the first irritation point and re-coupling in the second one, in-line Mach-Zehnder interferometer (MFI) and Michelson interferometer(MI) sensors have be demonstrated. To understand the mechanism underneath this coupling phenomenon, several parameters (laser power, laser lasting time, etc) tests are investigated. With bigger laser power and longer lasting time, one can obtain higher mode coupling, which is potential for greater sensitivity sensor. Combined with a long period fiber grating (LPFG), the cladding modes promoted in fiber cladding are studied. In some big power conditions, permanent deformation can be met on the irradiation points of the fiber. Although higher loss is induced, there is also other advantage, such like high temperature stability. The sensitivity and stability of temperature are discussed based on these sensors' configuration and mechanism. The experiences verify our laser irritation sensors can survive in very high temperature. When coating with some gas absorption film such like zeolite film, one reliable high sensitivity gas sensor is successfully demonstrated in low ppm vapor level.

This paper reports the development of surface modified ZSM-5 zeolite thin-film coated long-period fiber grating (LPFG) sensors for in situ detection of ammonia (NH(3)). The sensor was fabricated by growing MFI-type zeolite thin film (i.e. ZSM-5 with Si/Al ratio of 15) on the optical fiber grating by in situ hydrothermal crystallization. The sensor measures ammonia concentration by monitoring the molecular adsorption-induced shift of LPFG resonant wavelength (lambda(R)) in near infrared (IR) region. Upon loading the analyte (NH(3)) molecules, the refractive index of the zeolite film changes in the close vicinity of the fiber index where the LPFG has a large response to achieve high sensitivity. High sensitivity of this sensor also comes from the ability of the nanoporous zeolite to effectively concentrate the target molecules by selective adsorption. The sensor was capable of sensitive detection of ammonia at lower ppm level. The zeolite's internal surface was modified by ion exchange with NH(4)(+) followed by thermal treatments to enhance the surface acidity. The acidic ZSM-5 (i.e. H-ZSM-5) film exhibited higher sensitivity and improved selectivity for NH(3).

Small size fiber optic devices integrated with chemically sensitive photonic materials are emerging as a new class of high-performance optical chemical sensor that have the potential to meet many analytical challenges in future clean energy systems and environmental management. Here, we report the integration of a proton conducting perovskite oxide thin film with a long-period fiber grating (LPFG) device for high-temperature in situ measurement of bulk hydrogen in fossil- and biomass-derived syngas. The perovskite-type Sr(Ce(0.8)Zr(0.1))Y(0.1)O(2.95) (SCZY) nanocrystalline thin film is coated on the 125 microm diameter LPFG by a facile polymeric precursor route. This fiber optic sensor (FOS) operates by monitoring the LPFG resonant wavelength (lambda(R)), which is a function of the refractive index of the perovskite oxide overcoat. At high temperature, the types and population of the ionic and electronic defects in the SCZY structure depend on the surrounding hydrogen partial pressure. Thus, varying the H(2) concentration changes the SCZY film refractive index and light absorbing characteristics that in turn shifts the lambda(R) of the LPFG. The SCZY-coated LPFG sensor has been demonstrated for bulk hydrogen measurement at 500 degrees C for its sensitivity, stability/reversibility, and H(2)-selectivity over other relevant small gases including CO, CH(4), CO(2), H(2)O, and H(2)S, etc.

The thermal stability and flame retardancy of a new kind of rigid polyurethane (PU) foams/organoclay nanocomposites developed by our research group were investigated by using thermogravimetry analysis (TGA) and cone calorimeter test. Results indicate that compared with pure PU foams, rigid PU foams/organoclay composites show significantly enhanced thermal stability and flame retardancy. The reasons leading to the results were discussed in detail by relating with the morphology of the composites. The discussion suggests that the enhancement degree of thermal stability and flame retardancy of composites compared with that of PU foams coincides well with the sequences of gallery spacing of organoclay in the PU matrix.

We report a new method to measure the CO(2)-laser-irradiation-induced refractive index modulation in the core of a single-mode optical fiber for the purpose of design and fabrication of long-period fiber gratings (LPFGs) without applying tension. Using an optical fiber Fabry-Perot interferometer, the laser-induced axial refractive index perturbation was measured. We found that the CO(2)-laser-irradiation-induced refractive index change in the fiber core had a negative value and that the magnitude was a sensitive function of the laser exposure time following almost a linear relation. Under the assumption of a Gaussian-shaped refractive index modulation profile and based on the first two terms of Fourier series approximation, the measured refractive index perturbations were used to simulate the LPFG transmission spectra. LPFGs with the same laser exposure parameters were fabricated without applying tension, and their spectra were compared with those obtained by simulations.

This paper reports the development of a new zeolite thin film-coated long period fiber grating (LPFG) sensor for direct measurement of trace organic vapors. The sensor was fabricated by growing pure silica MFI-type zeolite thin film on the optical fiber grating by in situ hydrothermal crystallization. The sensor measures chemical vapor concentration by monitoring the molecular adsorption-induced shift of LPFG resonant wavelength (lambda(R)) in near infrared (IR) region. Upon loading analyte molecules, the zeolite's refractive index changes in the close vicinity of the fiber index where the LPFG has a large response to achieve high sensitivity.

Three different surface modifiers, octadecyl trimethyl ammonium (ODTMA), octadecyl primary ammonium (ODPA), and decanediamine (DDA) were used to modify Na+ - montmorillonite (MMT), and the resultant organoclays were coded as ODTMA-MMT, ODPA-MMT, DDA-MMT, respectively. Rigid PU foams/organoclay composites were prepared by directly using organoclay as the blowing agent without the addition of water. Investigation shows that the morphology of the nanocomposites is greatly dependent on the surface modifiers of clay used in the composites. In detail, DDA-MMT is partially exfoliated in the PU matrix with the smallest cell size, while two others are intercalated in the PU matrices with smaller cell sizes. The sequence of their cell sizes is pristine PU foams > rigid PU foams/ODTMA-MMT > rigid PU foams/ODPA-MMT > rigid PU foams/DDA-MMT, and the average cell size of rigid PU foams/DDA-MMT composites decreases evidently from 0.30 to 0.07 mm. Moreover, all rigid PU foams/organoclay composites show remarkable enhanced compressive and tensile strengths as well as dynamic properties than those of PU foams, and the enhancement degree coincides well with the relative extent of internal hydrogen bonding of materials and gallery spacing of organoclay. For example, in the case of rigid PU foams/DDA-MMT composite, 214% increase in compressive strength and 148% increase in tensile strength compared with those of pure PU foams were observed. ((C) 2007 Wiley Periodicals, Inc.

A novel method for preparing rigid polyurethane (PU) foam/organoclay nanocomposites was developed through the direct incorporation of an organoclay into PU foam matrices without the addition of any physical or chemical blowing agent. The resultant foams with an appropriate content of the organoclay had a finer cell structure than the pristine PU foams because the organoclay not only acted as a nucleating agent as expected but also acted as a blowing agent of the PU foams; this could be attributed to the bound water between the interlayers of the organoclay. In addition, the incorporation of the organoclay up to 4 phr resulted in improvements in the tensile and compressive strengths, with the maximum values appearing at 2 phr (110 and 152%, respectively). The significant improvement in the mechanical properties could be attributed to the finer cell structure and the increased internal strength of the materials due to the higher degree of hydrogen bonding. (C) 2007 Wiley Periodicals, Inc.

Emulsion polymerization in supercritical carbon dioxide is a green technology in the synthesis and process of polymer materials.Supercritical carbon dioxide is nontoxic,nonpolluting,easier to be separated,with rapid polyreaction speed and high selectivity.In this paper,the development and the latest advances in the emulsion polymerization in supercritical carbon dioxide are reviewde.It is figured out that supercritical carbon dioxide should be used in the emulsion polymerization to produce synthetic polymer materials without the toxic or volatiole organic solvent.It can reduce the environmental pollution,increase the performance of materials and simplify the process and production technology,with the widespread prospect in application.